This invention relates to multiple-wire cables, and more particularly to small gauge wiring for high frequencies.
Certain demanding applications require miniaturized multi-wire cable assemblies. To avoid undesirably bulky cables when substantial numbers of conductors are required, very fine conductors are used. To limit electrical noise and interference, coaxial wires having shielding are normally used for the conductors. A dielectric sheath surrounds a central conductor, and electrically separates it from the conductive shielding. A bundle of such wires is surrounded by a conductive braided shield, and an outer protective sheath.
Some applications requiring many different conductors prefer that a cable be very flexible, supple, or xe2x80x9cfloppy.xe2x80x9d In an application such as a cable for connection to a medical ultrasound transducer, a stiff cable with even moderate resistance to flexing can make ultrasound imaging difficult. However, with conventional approaches to protectively sheathing cables, the bundle of wires may be undesirably rigid. In addition, it is desired that the cable be relatively light weight, so that it does not require significant effort to hold an ultrasound transducer in position for imaging. Presently, ultrasound technicians loop a portion of the cable about their wrists to support the cable without it tugging on the transducer.
The need for flexible and lightweight cables is met by the use of very fine gauge wires. While effective, the process of manufacturing fine gauge coaxial wires is exacting and costly. To achieve the needed overall wire diameter, the center conductor and the helically-wound shield wires must be extremely fine, approaching the limits of practical manufacturability. While past cables for some uses have employed unshielded conductors, these are well-known to be unsuitable for applications such as medical ultrasound imaging that require high impedance, low capacitance, and very limited cross talk.
In addition, cable assemblies having a multitude of conductors may be time-consuming and expensive to assemble with other components. When individual wires are used in a bundle, one can not readily identify which wire end corresponds to a selected wire at the other end of the bundle, requiring tedious continuity testing. Normally, the wire ends at one end of the cable are connected to a component such as a connector or printed circuit board, and the connector or board is connected to a test facility that energizes each wire, one-at-a-time, so that an assembler can connect the identified wire end to the appropriate connection on a second connector or board.
A ribbon cable in which the wires are in a sequence that is preserved from one end of the cable to the other may address this particular problem. However, with all the wires of the ribbon welded together, they resist bending, creating an undesirably stiff cable. Moreover, a ribbon folded along multiple longitudinal fold lines may tend not to generate a compact cross section, undesirably increasing bulk, and may not provide a circular cross section desired in many applications.
The present invention overcomes the limitations of the prior art by providing a cable assembly that has a number of wires each having a central conductor and a surrounding insulating layer. Each wire is unshielded from the other wires, so that the conductor is the only conductive portion of the wire. Each wire has a first end and an opposed second end. The first ends of the wires are secured to each other in a flat ribbon portion in a first sequential arrangement, and the second ends of the wires are secured to each other in the same sequence as the first arrangement, with indicia identifying a selected wire in the sequence. The intermediate portions of the wires are detached from each other, and a sheath having a braided conductive shield may loosely encompass the wires, permitting significant flexibility of the cable.